Book I CONTAGION 25

deed act on one another, since they are not opposites, do never—
theless arouse the senses, though only by the mediation of the
qualities called spiritual. That the activity of these spiritual
qualities is powerful and a force in nature, is clear also, as I
have demonstrated in my work 'On the Sympathy and Antip—
athy of Things'. For they arouse both the senses and the
intellect, and are the principles of movement in animal bodies.
Again they seem to cause local movements, namely attrac—
tion and repulsion, and some of them even produce primary
qualities, for instance, *luminousness' generates heat.

Now that we have established these facts, we ask of those
who allege occult properties:  Since every activity comes
either from a substance or from a material or spiritual quality,
tell us by means of what principle occurs this activity by which,
as we see, contagions are produced? If they assert that it
ecomes into being from substance and from the shape of things,
why call it an occult property? " But let them call it what they
please, certainly shape, at any rate cannot produce anything
but loca!l movements up and down, rarefaction and condensa—
tion; never can it cause contagion, which is not per se a local
movement, but rather a corruption of certain things and a
generation of certain things. But if they assert that it comes
into being by means of some quality, then, if that quality be
material, they cannot designate any factor not known already,
unless perhaps they invent some unknown kind of quality
which is not heat, moisture or dryness, and this is quite im—
possible. But if they assert that the cause is some spiritual
quality, why then they could at least have used a familiar
term, and said outright that something spiritual produces
these contagions. But surely they cannot adduce that as a
cause; because these spiritual factors can only last just so long
as there is present the source whence they flowed, except in—
deed when they arise in the intellect. Whereas the factors
that carry contagion to a distant object endure just as well
even when the thing primarily infected is absent, and they
endure both in fomes and in the air; nay more, they are car—
ried from place to place even across the sea; this is a proof that
this something is a body that can be carried and endures even
when far from its place of origin.  But if they admit thatthis
something is certainly a body which is carried from place to
place, yet still assert that it acts by means of a spiritual quality,